Promising signs for wave barrier

A wave barrier that was established at Te Waihora/Lake Ellesmere recently is showing positive signs for the successful establishment of macrophyte beds.

David Murphy, Programme Manager, Whakaora Te Waihora, says that test results have been very promising to date.

“In October, test results showed that the wave barrier was effective in consistently reducing wave height by 20-40%. This allowed us to progress to the next stage of re-establishing macrophyte beds in the lake,” he says.

The 100metrelong wave barrier that was established on the south western side of Te Waihora last September, and is believed to be a first of its kind in the world. It is hoped that it will reduce wave damage, and protect and enhance the ability of macrophytes to embed in the lake.

David Murphy says large beds of macrophytes were historically found in Te Waihora but haven’t been present in the lake since the 1960s.

“Macrophyte beds have the ability to buffer wave action, take up nutrients, improve water quality and provide diverse habitats for fish and wildlife. This is why one of Whakaora Te Waihora’s goals is to re-establish these macrophyte beds,” he says.

In January, NIWA scientists took the next step in the project and undertook the most critical part of the trial – diving in to plant the macrophytes in the lake, which were transported from their nursery in Taumutu.

Using a hand-auger to dig holes in which the macrophytes were planted.

NIWA ecologist Mary de Winton says “whānau from Taumutu Marae have offered extensive local knowledge on the lake and its history, and have shown researchers the best places to source seeds and plants, including from the neighbouring Halswell River.”

Now that the macrophytes have been planted, they will be closely monitored to see if they can embed.

“I am very hopeful they will embed given the reduction in wave height the barrier has created,” says David.

The floating wave barrier comprises 59 New Zealand Oregon logs, each 10m long. The logs are arranged three deep side-by-side, with the remainder placed in a triangular pattern to brace the structure. This is anchored to the lake bed in several places with a cable running the length of the barrier to hold it in place.

One additional wave barrier is planned for installation on the lake this year.